# Data sources

Every value on the map comes from the public datasets below. Nothing is estimated or filled in: if a source has no value for a county, the app shows "no data" and leaves that county out of the top 5 when you've weighted that layer. Processing: `scripts/build_data.py`, then `scripts/counties_geojson.mjs`, `scripts/build_layers_v2.py` and `scripts/build_layers_v3.py`, produce `data/counties.json` and `data/state_tax.json` (also copied to `public/data/`).

| Layer / field | Source | Vintage | URL |
|---|---|---|---|
| County boundaries | us-atlas v3.0.1 (Census Bureau cartographic boundary files, 1:10m) | 2017 boundaries | https://cdn.jsdelivr.net/npm/us-atlas@3.0.1/counties-10m.json |
| Median gross rent (`rent`) | US Census Bureau, American Community Survey 5-year, table B25064 (table-based summary file) | 2019–2023 | https://www2.census.gov/programs-surveys/acs/summary_file/2023/table-based-SF/data/5YRData/acsdt5y2023-b25064.dat |
| Median household income (`inc`) | ACS 5-year, table B19013 | 2019–2023 | https://www2.census.gov/programs-surveys/acs/summary_file/2023/table-based-SF/data/5YRData/acsdt5y2023-b19013.dat |
| Households with broadband of any type (`bb`) = B28002_004 ÷ B28002_001 | ACS 5-year, table B28002 | 2019–2023 | https://www2.census.gov/programs-surveys/acs/summary_file/2023/table-based-SF/data/5YRData/acsdt5y2023-b28002.dat |
| Connecticut rent / income / broadband | ACS 5-year 2017–2021 (the last release using CT's 8 legacy counties; 2022+ uses planning regions that don't match the map's boundaries). Labeled per-county in the app. | 2017–2021 | https://www2.census.gov/programs-surveys/acs/summary_file/2021/table-based-SF/data/5YRData/ |
| Avg summer high (`tmax`) = mean of Jun/Jul/Aug monthly mean max temp, 1991–2020 | NOAA NCEI nClimDiv county dataset (`climdiv-tmaxcy-v1.0.0-20261006`) | 1991–2020 avg | https://www.ncei.noaa.gov/monitoring-content/data/us/climdiv/monthly/current/ |
| Avg winter low (`tmin`) = mean of Dec/Jan/Feb monthly mean min temp, 1991–2020 | NOAA NCEI nClimDiv (`climdiv-tmincy-v1.0.0-20261006`) | 1991–2020 avg | same as above |
| Disaster expected annual loss rate, national percentile (`alr` = `ALR_NPCTL`), overall risk score/rating (`risk`, `riskR`), per-hazard risk ratings (hurricane, wildfire, inland flooding, coastal flooding, tornado, earthquake), population (`pop`) | FEMA National Risk Index, county table | v1.20, December 2025 | https://www.fema.gov/about/reports-and-data/openfema/nri/v120/NRI_Table_Counties.zip |
| Median home value (`hv`) | ACS 5-year, table B25077 (CT: 2017–2021) | 2019–2023 | https://www2.census.gov/programs-surveys/acs/summary_file/2023/table-based-SF/data/5YRData/acsdt5y2023-b25077.dat |
| Summer dew point (`dew`) = mean of the Jun, Jul and Aug 30-year normal mean dew point grids, averaged over the 4 km cells inside each county (cells touching the county for tiny counties), °C converted to °F | PRISM Climate Group, Oregon State University, 30-year normals `tdmean`, 4 km (`prism_tdmean_us_25m_2020{06,07,08}_avg_30y`) | 1991–2020 normals | https://data.prism.oregonstate.edu/normals/us/4km/tdmean/monthly/ |
| Annual snowfall (`snow`) = `ANN-SNOW-NORMAL` (inches) averaged over the NOAA stations inside the county. If none, the nearest station within 40 km (station name and distance shown in the app). Trace values count as 0. | NOAA NCEI U.S. Climate Normals, annual/seasonal, by station (v1.0.1) | 1991–2020 normals | https://www.ncei.noaa.gov/data/normals-annualseasonal/1991-2020/archive/us-climate-normals_1991-2020_v1.0.1_annualseasonal_multivariate_by-station_c20230404.tar.gz |
| Jobs in your field (`j`): annual average employment summed over all ownerships (federal, state, local, private), and location quotient = (county industry jobs ÷ county total covered jobs) ÷ (same ratio for the US) | BLS Quarterly Census of Employment and Wages (QCEW) open data API, 2025 annual averages. NAICS 21, 22, 31-33, 51, 52, 54, 5415, 61, 62; totals from industry 10 | 2025 | https://data.bls.gov/cew/data/api/2025/a/industry/{code}.csv |
| Avg weekly pay in your field (`j[...][2]`) = QCEW total annual wages ÷ annual average employment ÷ 52, summed over the disclosed ownerships. If BLS withholds the industry, the app uses the county's all-industry average weekly wage (`wAll`, industry 10, all ownerships) and marks the county "partial". | BLS QCEW open data API, 2025 annual averages | 2025 | https://data.bls.gov/cew/data/api/2025/a/industry/{code}.csv |
| Average commute to work (`com`) = B08013_001 (aggregate travel time to work, minutes) ÷ B08303_001 (workers 16+ who did not work from home) | ACS 5-year (CT: 2017–2021, as with the other ACS fields) | 2019–2023 | https://www2.census.gov/programs-surveys/acs/summary_file/2023/table-based-SF/data/5YRData/acsdt5y2023-b08013.dat and `...-b08303.dat` |
| Nearest ski area (`skiMi`, `skiNm`) = great-circle miles from the county's 2020 center of population to the nearest ski area. A ski area is (a) a named OSM `landuse=winter_sports` feature with at least one ski lift (`aerialway` = chair_lift, gondola, t-bar, platter, drag_lift, j-bar, rope_tow, magic_carpet, mixed_lift) within 5 km, or (b) a cluster of 2+ named lifts within 2 km that isn't near a named area (shown as "unnamed ski area (N OSM-mapped lifts)"). Abandoned/disused lifts and water-ski, wake and water-park cables are dropped. 551 ski areas; list in `data/ski_areas.json`. | © OpenStreetMap contributors, Open Database License (ODbL) 1.0, via the Overpass API (downloaded Nov 8, 2026) | Nov 2026 snapshot | https://www.openstreetmap.org/copyright, https://overpass-api.de/ |
| Terrain relief (`rel`, feet) = 98th percentile minus 2nd percentile elevation of all DEM cells within 50 km of the county's 2020 center of population (percentiles rather than max/min so a single tower or bad pixel can't set the value) | USGS 3D Elevation Program (3DEP) seamless DEM, resampled by USGS's 3DEPElevation ImageServer to a 0.01° grid (≈1 km) in EPSG:4326; four exports (CONUS west, CONUS east, Alaska at 0.02°, Hawaii). Cells below −90 m treated as no data. Public domain. | Fetched Nov 8, 2026 (3DEP seamless, current) | https://elevation.nationalmap.gov/arcgis/rest/services/3DEPElevation/ImageServer/exportImage |
| County centers of population (for ski distance and terrain) | US Census Bureau, 2020 Centers of Population by County (1 county without one, Valdez-Cordova AK, uses its polygon's interior point) | 2020 | https://www2.census.gov/geo/docs/reference/cenpop2020/county/CenPop2020_Mean_CO.txt |
| State income tax brackets (single filer) | Tax Foundation, "2026 State Income Tax Rates and Brackets" (rates as of Jan 1, 2026) | 2026 | https://taxfoundation.org/data/all/state/state-income-tax-rates-2026/ |

## Method notes
- **Rent vs income** = county median gross rent × 12 ÷ the income you enter.
- **State income tax** = the single-filer marginal rate for the bracket your gross income falls in (ignores deductions, credits and local income taxes such as NYC or Ohio municipal taxes). Washington is set to 0% because the Tax Foundation table notes it taxes capital gains only, not wages.
- **Disaster loss** uses FEMA's Expected Annual Loss *rate* percentile (loss relative to the value exposed), not the overall Risk Index score, because the overall score scales with how much property a county has, which makes every big metro look "very high risk".
- **Fit score** (0–100) = weighted average of per-layer scores: rent 10%→1, 40%→0 of income; summer high 72°F→1, 100°F→0; winter low 40°F→1, 0°F→0; loss-rate percentile 0→1, 100→0; broadband 95%→1, 60%→0; state rate 0%→1, 10%→0. Map colors show your rank among counties still in play.
- **Home prices** = median home value ÷ your income (2× → 1, 6× → 0). The dealbreaker is a dollar cap on the county median.
- **Winter cold** and **snowfall** each have a direction. Winters: mild (40°F lows → 1, 0°F → 0) or cold (−10°F → 1, 30°F → 0). Snow: less (0 in → 1, 60 in → 0) or more (80+ in → 1, 0 in → 0).
- **Humidity** = summer dew point: 50°F → 1, 70°F → 0.
- **Jobs** score = 0.6 × location-quotient part (LQ 0.25 → 0, 4 → 1, on a log scale) + 0.4 × job-count part (1 → 0, 100,000 → 1, on a log scale). The dealbreaker is a minimum job count. When BLS suppresses every ownership type for a county, it shows "suppressed" and is treated as missing. When only some are suppressed, the count is a minimum (shown with "+"). A county with no row in the QCEW file has 0 covered jobs in that industry.
- **Pay** score: $700/wk → 0, $2,500/wk → 1 (linear). The dealbreaker is a minimum weekly pay. **Ski** score: 0 mi → 1, 150+ mi → 0. **Commute** score: 15 min → 1, 40 min → 0.
- **Terrain** score = log(relief ÷ 200 ft) ÷ log(25), clamped: 200 ft or less → 0, 5,000 ft or more → 1. The dealbreaker is a minimum relief (default 2,000 ft). The AI uses terrain for "mountains / hiking / hills" and ski distance only for skiing. Examples: Eagle CO 5,388 ft, Harris TX 202 ft, Miami-Dade FL 10 ft.
- **AI daily cap:** the AI box is capped at 35 runs per UTC day for the whole site (plus 30 per visitor per hour). One run is two Llama 3.3 70B calls, measured at ≈145–150 neurons, so the cap uses ≈5,250 of Workers AI's 10,000 free neurons per day. The counter is a SQLite Durable Object (Worker `whereshouldimove-cap`, free plan), which counts reliably; KV was tried first but its cached reads let it overcount. When the cap is hit the box says so and the sliders keep working.
- **Share:** "Share image" draws a 1200×630 PNG in the browser from the current map, top 5 and title. "Copy link" puts every setting in the URL hash, so the link reopens the same map.
- **Not used:** Zillow ZHVI. ACS B25077 covers every county, and I didn't want to redistribute Zillow data without checking their terms.

## Known gaps
- Terrain: relief is measured around the population center, so a county with a big range at its far edge can score low. Hawaii uses the island chain's mean center for some counties. A ≈1 km grid smooths out small cliffs.
- Ski areas: OSM is volunteer-mapped. Some small hills are missing or only appear as unnamed lift clusters, and some nordic-only centers are left out because they have no lifts. Distances are straight-line, not driving.
- Connecticut: no FEMA NRI values (NRI v1.20 uses CT planning regions, not the 8 legacy counties on this map).
- Valdez-Cordova, AK (split in 2019), Lexington city, VA and DC: missing in one or more source files.
- Hawaii: not covered by nClimDiv temperature data. Alaska and Hawaii: not covered by the PRISM CONUS dew point grid.
- Snowfall: 61 counties have no NOAA station normal within 40 km ("no data").
- QCEW 2025 annual averages are the latest BLS release. Small counties are often suppressed for single industries, oil & gas especially.